Textile fabrics containing neomycin



2,830,011 7 v TEXTILE FABRICS CONTAINING NEGMYCIN Robert P. Parker, Ridgewood, and Anthony Abbey, Jamesburg, N. J., assignors to American Cyanamid Company, New York, N. Y., a corporation of Maine No Drawing. Application February 7, 1957 Serial No. 638,695

12 Claims. (Cl. 167-84) This invention relates to a durable textile finish containing neomycin, to processes of using said finish and to articles made of textile fibers having been treated by the finish whereby neomycin is uniformly adhered to the fibers thereof and are capable of a continuing antibacterial action over extended periods of time and possess re-usahle utility and antibacterial activity after irioning, washing, and other cleaning operations. This application is a continuation-in-part of out application Serial.

No. 482,392, filed January 17, 1955, now abandoned.

In recent years, increased attention has been given to the development of textile finishes which have become known as purifying finishes. These are intended to reduce the number of microorganisms residing on'the material whereby such materials may be used with less danger from harmful bacteria. These purifying finishes when applied to articles of clothing worn close to the body are also helpful in preventing the development of body odors.

A satisfactory purifying finish should be durable and active at low concentrations against, a broad spectrum of microorganisms. allergenic. It should not have the tendency to sensitize the wearer of the textile fabric to the material of 'the finish. It should not have the property of allowing strains of bacteria to develop which are resistant to the antibacterial agent of the finish. It should impart .little' or no color to the fabric and should be stable with respect to color and activity for many monthsunder storage and shipping conditions. It should be resistant to home laundry conditions and to commercial laundry and dry cleaning operations. It should impart little or nomodification of the hand of the textile. It should be substantitive to the fibers and be compatible with dyes and resin-containing textile finishes. The textile finish of the presentinvention rates very high'in each of the qualifications just mentioned.

Various textile purifying finishes containing antibacterial substances such as hexachlorophene, tetrachlorophene, quaternary ammonium compounds such as dimethyl benzyl ammonium chloride, metal complexes of.

mercury, copper'and silver, organic compounds and others have been used but are for the most part nondurable ,andunsatisfactory in other respects.

Antibiotics have previously been employed to coat or impregnate various materials inorder to induce therein desirable bacteriostatic or bactericidal properties. a For example, surgical dressings, gauze bandages and the like have been treated with tetracycline, chlortetracycline, oxytetracycline, tyrothricin, bacitracin, chloroamphenicol, etc.; but such materials have been limited to single-use purposes and havefnecessarily been discarded or thrown away following such single use. This, of course, was due to the fact that the antibiotics were not sufiiciently stable or substantive to the base materials and consequently could not remain in active'antibacterial form therein following cleaning operations prior to reuse.

It should be non-toxic and nonadhered on the fibers thereof a suflicient concentration of neomycin whereby such material possesses antibiotic activity for an extended time with such activity surviving cleansing operations.

It has been found that neomycinmay-be readily applied to textile fibers, is substantive thereto and will impart to such articles made therefrom antibiotic properties which will remain after cleansing operations or manufacturing and finishing processes, even at elevated temperatures.

Neornycin is an antibiotic discovered by Waksman and Lechevalier and is produced by a strain of Streptomyces closely related to .Stretpomyces fradiae (ATCC No. Science, March. 25, 1949, volume 109, pp. 305-.-' 307. It is a basic compound, freely soluble in water, possesses a wide antibacterial spectrum, is generally nonirritating and non-sensitizing and bacterial resistance to it develops very slowly. The term neomycin is used herein in its ordinary sense to denote the commercially available product which ,is called'neomycin, it actually being a mixture of two very closelyrelated antibiotics known more specifically as neomycin B and neomycin C. The term is also intended to cover neomycin as just de fined, the individual components of the complex or its salts of which the sulfate is most generally available,

neomycin aconitate, neomycin phthalate, neomycin. un-. decylinate, neomycin palmitate, neomycin stearate and.

others.

v The exact nature ofthe; chemical reaction or physical, attraction of the neomycin and the fibers and the precise.

mechanism whereby the antibiotic becomessubstantive to the base material is not completely understood; but the phenomenon of substantivity has been clearly indicated with a broad range of materials. The invention is particularly useful with fibers of cellulosic origin. Included in this group as illustrative but not limitative are cotto n, regenerated cellulose, cellulose acetate, wood fibers, linen, jute,'ramie, hemp, and other fibers used in the making of textiles, cordage, paper, paper board, and the like. The

purifying finish of the present invention may also be applied to good advantage to proteinaceous fibers such aswool, silk, and the synthetic polyamide fibers which are sold under tradenames such as Nylon 66 and Perlon, and.

also the caprolactams such as Nylon 6. The present .in-

vention is also concerned with the treatment of the acrylic fibers such as Orlon (polyacrylonitrile), Creslan and Acri:

lan (acrylic tripolymers), andDynel (a copolymer of vinyl chloride and -acrylonit1ile). Also synthetic fibers of the polyester type maybe treated with the neomycin.

finish of the present invention to'provide a durable antibacterial finish. Among these may be mentioned Dacron and Terylene (polyesters of terephthalic acid and ethylene Other miscellaneous synthetic fibers which may; be used with the purifying finish of the present invention In addition to mineral fibers" glycol) include Saran, apolyvinylidene chloride. these synthetic fibers, naturaland synthetic Patented Apr. 8, 1958 a percent by weight kerchiefs, diapers, hand, dish and bath towels, books and. book covers, washable cloth toys, dolls and similar play-j things; hospital and hotel sheets, and pillow cases,.hospital and examination room bathrobes and slippers, barbers and .beauticians cloths, papertissue, diaper liners and 'catamenial bandages, and. similar fibrous articles used in commerce and comingin contact with the general public.

The concentration of the neomycin in the materials may be varied within widelimits depending on the use to which the particular materialis intended. Useful results are obtainable when the fabric contains as little as 0.0001 of neomycin; j The preferred range varies from about neomycin based on the weight of the fabric. For prophylactic purposes, deposition of from about 0.05 microgram up to micrograms per square centimeter has been found satisfactory with preferred commercial ranges lying between about 0.1 and about 6 micrograms per square centimeter.

The neomycin may be readily adsorbed and substantivelyadhered to the fibrous base materials by padding, exhausting, spraying or by other techniques which are practiced in the art whereby the solution containing neomycin is brought into contact with the fibers for a sufficient period of time to become substantively adhered to the base.- When applying by exhaustion of the neomycin from a solution, it has beenfou n d that a period of time fromaboutS minutes to'about 60 minutes or more is sufiicient to enable substantially all of the neomycinto become substantively adhered to the base. Thebase is then rinsed, preferably two. or three times, in order to remove any excess treating solution and it is then dried at'room temperatures or more rapidlyat elevated temperatures as high as 350 F. The materials are then found to have all of the neomycin present substantively adhered to' the base. V i 5 i When making fibers produced by a felting process as in the manufacture of paper, the neomycin may be added to the heater or associated with the fibers at a step prior to the felting operation. The faet'that neomycin is substantive to cellulose fibers to ahigh degree makes it possible to apply the antibiotic without additional equipment in the paper-making process without loss of the expensive antibiotic in the white water. In addition, this leads to an-important advantage of the invention which is the fact that the neomycin is uniformly distributed through 0.01 percent to 1 percent by weight of cific illustrations of sueh'articleswould include: handliquid and then dried. When applied by exhausting, the solution may contain as little as 0.001 microgram per milliliter of solution when highly adsorptive cellulosic fibers are treated. From 5 to 500 micrograms of neomycin per milliliter is' considered a preferred range for application by exhaustion. For normal prophylactic purposes, suiiicient concentrations of neomycin may be substantively adhered to base materials from aqueous treating solutions containing from about 1 microgram to about 400 micrograms per milliliter with preferred commercial limits lying between about 2 and about 200 micrograms per milliliter.

' weight of sodium metabisulfite or citrate, for instance. Itmay also contain other substances.

such as antifungal agents, colors, brighteners, wetting agents, softeners, odors, and the like.

The invention will be further illustrated in more specific detail by the following tests and related examples.

It should be understood, however, that although these tests and examples may describe in more particular detail some of the very. specific features of the invention, they are given primarily for purposes of illustration and the invention in its broader aspects is not to be construed as limited thereto.

EXAMPLES 1., 2, AND 3 in distilled waterat room temperature and then air-dried before use in the various tests. Swatches of the cloth measuring approximately 17.5 cm. x 13.5 cm. and weighing approximately 2.5 grams each were used. v

The various antibiotics were tested on a weight basis at concentrations of Zmicrograms and 20 micrograms per; milliliter in distilled water, unless otherwise specified. Approximately milliliters of solution of the antibiotic was employed for treating each 2.5 gram test sample of cotton cloth. 7 i The cloth swatches were labeled, folded and placed in screw-cap jars containing the antibiotic treating solutions employed. The jars were then placed in a heated waterbath maintained at the temperature indicated in the particular table and held for'approximately 30 minutes with out the entire fabric and .is not located merely on the surface or a particular area thereof. 7

-If desired, the neomycinmay be dissolved in other solvents such as methanol, butanol, or other organic solvents; but such normally introduces increased production costs and is not commercially desirable.

The concentration of the neomycinin the treating solumixing .and agitation every 10 then removed from thewater-bath and the antibiotic solutions were decanted and minutes. The jars were held for assay. The cloths were imrnediately rinsed three times in tap water at room temperature bydipping three times in each water rinse in the jar and then squeezed and wrung out by hand. Sample discs approximately 10 to 11 millimeters in diameter were removed using an ordinary cork borer and not less than eight discs were tested for each cloth. Each 10 to 11 millimeter cloth disc appeared to absorb approximately 0.033 milliliter of solution and measured approximately 0.94square cm. The clothdiscs were dried for approximatelyone hour at 3 7 C. ,and then placed on suitable testplates', with the results shown in Tables I,

* II, and III.

each Pyrex No. 3162 fiat-bottomed dish provided with The plates were permitted to before applying the test discs.

an unglazed ceramic lid. solidify at leflSt, 20 minutes I T Assay Procedures (18. hours-37 C.)

treating solution of 20 This table is deemed to be i A Antibiotics Test organism Medium Neomycin B. subtilis No. 6633 Difco nutrient agar 0.5% N e01 adj. to pH 8.0. Chlortetracycline gxg tetrg elinen B. subtilis No. 6633 Difco nutrient agar ad to pH 6.0.

6 acy 9- Polymyxin B ulfat Br. bronchiseptica No. 4617".-. B. B. L. trypticase soy broth 1.5% agar 1.0% Tween "80." Patulin E. coli 9637".-.- Difco nutrient agarpI-I 6.0. I Bacitracin M. flavus POI N o 16 Difco pen. seed agar pH 6.8. Tyrothrictunuum do Dlfco pen. seed agar propyl. glycol. Chloramphemeo1. S lutea N o. 9341 Difeo pen. seed agar pH 6.8. Penicillin B. subtilis No. 6633 Difco nutrient agar 0.5% N 2101 ad to pH 6.8. Erythromycin S. Zu'tea N o. 9341 Difco pen. seed agar pH 8.0.

TABLE 1 Consideration of Table n drastically indicates the [Substantivity of various antibiotics at 52 0.; 2 meg/ml. treatment] marked superwrlty of t e spbstantlvlty 0f e my 1- fate over the other antibiotics tested. I In this case, neo- Antibiotic Meg/disc mycin sulfate possessed substantivity almost thirteen times cm?) 20 that of the second best antibiotic at a temperature of 95 C. and a concentration of Neiimycm Sulfate 128 micrograms per milliliter.

h hlid 0.064 iiigifiife iit dr ii afif 0.050 the most indicative of the superiority of neomycin sulfate g gg 8-83? inasmuch as such temperatures and concentrations are P l ymyiun issuers.-. 0.' 017 closest to that found in the industry; 1 th? fift 3888 a 8. 111 C S a e ohioramph enicol 0. 000 EXAM LE 4 Consideration of Table I indicates the marked superiority of the substantivity of neomycin sulfate over the other antibiotics tested. Itis to be observed that the substantivity of neomycin sulfate was approximately twice that of the second best antibiotic at a temperature of' 52 C.

TABLE II [Substantivity of various antibiotics at 95? 0.; 2 meg/ml. treatment] Antibiotic Meg/disc (0.94 cm!) Consideration of Table II even further indicates the marked superiority of the substantivity of neomycin sulfate over the other antibiotics tested. It is to be observed thatthesubstantivity ofneomycin sulfate was approximately five times that ofthe second best antibiotic at a temperature of 95 C. This temperature is deemed to be more indicative of the true superiority of neomycin sulfate inasmuch as such higher temperature is closer to cleaning and sterilizing temperatures than that of the preceding tests at 52 C.

The methods set forth in the description of Examples 1, 2, and 3 were "carried out substantially as set forth therein with the sole exception that dyed cotton was substituted for the white cotton cloth in order to determine if the dye would interfere with the substantivity of the neomycin to the cottonfabric. The results were substantially as set forth in Tables I, II, and III, thus indicating no interference with the substantivity characteristic.

EXAMPLE 5' The methods set forth in the description of Examples 0 1, 2, and 3 were also applied to linen fabrics and the testing conditions were carried out under similar conditions as indicated for cotton, with the exception that anironing test at a temperature of approximately 190 C. wasadded. The substantivity tests indicated results very comparable to that set forth in Tables I, II and III and the ironing tests merely reduced the concentration of theantibiotic (neo-' mycin sulfate) by 30 percent; the samples prior to ironing containing 0.1 microgram per square centimeter amine samples after ironing containing 0.07 microgram per square centimeter.

about two hours.

EXAMPLE 6 Evaluations of the substantivity of neomycin sulfateto cotton cloth were carried out in washing machine tests as follows:

White cotton cloth (approximately 80 x 80 count) measuring approximately 13.5 inches square and weighing approximately 10 cloth squares twice with hot tap water and then dried at 175 100' squares) were weighed out, rinsed C. for A Bendix automatic washer, model 3-211, wasused and the water temperature dial was set at the hottest point whereby the entering hot tap water I had a temperature of approximately 58 C. The water quantity dial was set at low whereby approximately 4.5 gallons (17.1 liters) was used.

Neomycin sulfate (700 micrograms base per milli-' gram) was used on a weight basis of 34.2 milligrams neomycin for 17.1 liters of water (approximately-2 micrograms per milliliter). f;

The kilogram of cotton cloth squares was divided into five equal parts and each part separately loaded into the machine and tested. The cycle was initiatedin e h grams each were used;- One kilogramof' series by a 13-minute soaking period followed by a-washing, rinsing and spin dry period of 35"minutcs. The

34.2 milligrams of neomycin were ing cycle. i

The treated cloths were randomly sampled by removing -11 mm. diameter discs (approximately 0.94pm.?) with a cork borer and were tested for activity by the B. subtilis plate method previously described. The results are tabulated below.

The Bendix cycled cotton cloths were'sainplcd imme diately after the washing and assays indicated that there remained approximately 0.097 rnicrogram per disc or 9700 micrograms per kilogram of cloth. The cloths were then air dried and ironed by hand at a temperature of approximately 175 C. Assays of the ironed cloths indicated that there remained 0.061 microgram per disc or 6100 micrograms per kilogram of cloth.

added during the soak- EXAMPLE 7 press section and then dried swatches weighing 2.5 grams each were used in 50 milliliters of aqueous solution 7 approximately 10-11 mms. diameter (actually 0.94 cm?) were cut fromthe swatches and assayed as described previously.

Solu- Swatch .Per- Solution, Disc, total cent Antibiotic tion, total mgm./O.94 rngms. activmgmJ mgms. em. antiity on ml; antibiotic swatch biotic Neomycin sulfate..... 1, 000 4. 2 1, 000 100 o 2 100 0. 4 100 100 Neomycin p-hydroxynzoate 20 1, 000 2. 4 600 G0 Neomycin N tartrate 20 1, 000 2. 2 55 55 Do 2 100 0.2 50 Neomycin proplonate. 20 1,000 2. 7 680' 68 D0 2 100 0. 2 50 50 Neomyctn aconitate 2 100 0.22 55 Neomycin lsonicotinate 2 100 0. 24 00 Neomycin phtha1ate-. 2 0.2 50 50 EXAMPLE 8 Cotton fabrics treated as set forth in Table III and containing approximately 1.39 micrograms'per square centimeter were made up into handkerchiefs and then sterilized by exposure to heat at 175 C. for two hours. These handkerchiefs wereiused under normal conditions and were found. to remain in a sterile state when incontact with a limited number of bacteria'such' as might be found in the air from effluvium, scattered nasal secretions, and'the like. After being used, the handkerchiefs were washed'in a Bendix washer and dried andiironed at normal ironing temperatures (175 C.)' and it was established that the handkerchiefs still possessed substantial antibacterial activity.

EXAMPLE 9 -A high g radebleached sulfite pulp which had been of neomycin. Discs measuring C grams per milliliter of total pulp volume) with agitation for approximately 20 minutes. The neomycin-pulp was then felted on a Fourdrinier wire, pressed lightly in a on a Yankee drier having a diameter of 14 feet approximately and operating at a surface temperature of 250 C..

The dried continuous paper web was then processed, cut, folded and packaged. Representative samples selected at random. after the drying were tested and indicated the presence of antibacterial activity.

EXAMPLE 10 EXAMPLE 11 To 100 milliliters of an aqueous solution containing 19 micrograms per milliliter of neomycin was added a l-gram swatch of 80 x 80 cotton percale and shaken at 35.4 C. for 48 hours. The fabric was removed from the solution, rinsed with water and dried. On analysis, the fabric was found to have adsorbed thereon 0.17percent by weight of neomycin. Less than2 micrograms per milliliter .of the neomycin remained in the solution.

This test demonstrated an 89.5 percent exhaustion of the neomycin from the solution by adsorption on the cellulosic fibers as a result of the treatment.

EXAMPLE 12 EXAMPLE 1s A textile finishing solution comprising water having V dissolved therein 0.1 percent by weight of neomycin added as neomycin sulfate and 0.02 percent by weight of so-' dium metabisulfite was prepared. This solution was applied to a group of textile fabrics by padding with picklightlygrefined .in continuous refiners was treated with sufficient neomycin sulfate (approximately 20 microtip of the finishing solution ranging from 60 peroent to 100, percent. The treated fabrics were then dried at 225 F. for two minutes and tested for antibacterial activity against S. aureus. These fabrics were then washed in a Westinghouse Laundromat washing machine with the water at F. and containing 0.10 percent by weight of neutral soap chips. The machine was operated on a fifteen-minute washing cycle with two 15-minute rinses making a total washing cycle of 45 minutes. The fabrics were then dried at 225 C. for two minutes as before and tested for antibacterial activity. The results of these tests are shown in the followingtable.

The test'organism used was Staphylococcus aureus,the

size of the cloth discs was 11.5 mm., and 'a test zone larger than this indicates-definite antibacterial activity.

The letter P- stands for partial, S slight, VS very slight,

Zoneof Percent Number inhibineoof tion 1 Fabric mycin 'laund. against in cloth washes Staph. aureus,

21.1 Nylon tafleta 0.10 V j 5' 12.0 p 18.8 Acetate'-taneta;;. r 0.10 g e 5 vs 21.7 1 18.6 Rm: n ma-re 1 2 $3 10 17.0 25 16.8 v 20.3 Rayon challis "1. v0.06 1%: 5 16.8

. p 18.4 Woolflarinel-.. 0.08 g 6 O 20.4 -1 16.9 50/50 viscose/acetate 0.10 2 8 I 1 10 16.2 25 14.1 I: Z 20.0 D

v 0416 E1? 5 11.1 v 18.1 rlon.... 0.08. j 8

i s vs,

V p H a 20.0 mdmir t.'. .;i;..- 0.10 i

I 19.5 1 17.0 5 16.5 Cotton,80x80 percale 0.10 2 12:8 25 14.9 50 12.4 18.5 Dynel 0.10 y g 6 PC 17.7 a 1 16.6 05 35 dacron/cotton shitting 0.06 g 7 13:2 15.3 25' 0 EXAMPLE 14 Swatches of wool flannel, 80 x 80 cotton percalc, ny-

dry cleaned by the dry cleaning method in use 'in that establishment. The fabrics were then testedfor antibacterial'activity against E. coli and S. aureus and it was found that the original antibacterial activity was substantially unchanged as a result of the dry cleaning operation. The antibacterial activity which survived after repeated commercial dry cleaning operations is shown in the following table.

Zone of in- Number of hibitlon cleanings Fabric I p Initial.--" Cotton percale Rayon challis Wool flannel 1 Nylon sheer;

7 EXAMPLE 15 To evaluate the effect of contact with acid or alkaline 10 gm. NaCl 4 4)2 a 1 gm. ortho-Na HPO dissolved in 1 liter of water. The acid solution consists EXAMPLE 16 To determine the effect of light on the antibacterial properties of treated cloth, x 80 cotton percalc was treated with 0.1 percent neomycin by padding, dried for two minutes at 225 F. and exposed in an Atlas Fade- Ometer. The data shown in the table below indicates little effect of light on the antibacterial activity after as much as 80 hours exposure.

Zone of inhibition against Staph. aureus, mm.

Hours of exposure in Fade-Ometer EXAMPLE 17 0.1 percent neomycin, was exposed for 15 minutes in a I steam sterilizer at 250 F. The zone of-inhibition to S. aureus was'decreased only from 19.4 to 18.6 mm. by this treatment.

I1 EXAMPLE 18 The effect of dry heat on treated fabric was demonstrated by placing a swatch of 80 x80 cotton percale treated with 0.1 percent neomycin between two metal plates heated at 365 F. and allowed to remain there for ten minutes. of inhibition was decreased only from 19.4 to 16.1 mm.

We claim:

l. A method of imparting a durable antibacterial finish to textile fibers which comprises the stepsof bringing said fibers into contact with an aqueous solution containing from at least 0.0001 percent by weight of neomycin and thereafter drying said fibers.

2. A method of finishing textile fabrics to impart a durable antibacterial activity thereto which comprises padding said textile fabric. with an aqueous solution. containing at least 0.001 percent by weight of neomycin and thereafter drying said fabric.

3. A method of making felted cellulosic articles having a uniformly dispersed antibacterial activity throughout which comprises the steps of dispersing cellulosic fibers in an aqueous suspension containing at least 0.0006 percent of neomycin and thereafter draining off the aqueous solution from said fibers and felting the same on a screen, and drying said feltedcellulosic fibers.

. 4. A method of finishing textile fabrics containing cot ton fibers to impart-adurable antibacterial finish thereto which comprises thersteps of wetting said fabric with a solution containing at least 0.0006 percent by weight of neomycin and thereafter drying said fabric.

5. A method of finishing fabrics containing cellulosic fibers which comprises the steps of co-ntactingsaid fabric with an aqueous solution containing at least 0.0001 per-.

cent by weight of neomycin; allowing the aqueous solution to remain in contact with said cellulosic fibers fora period of at least five minutes, removing the fabric from the aqueous finishing solution and drying to obtain a fabric having durable antibacterial activity distributed uniformly throughout.

6. A dry textile fabric having a durable antibacterial finish resistant to washing with water comprising cellulosic fibers. having uniformlyadsorbed thereon neomycin As a result of this treatment, the zone fibers having u in amounts such that the fabric contains atleast 0.0001

percent i yi h of neomyc n:

7;; A dry'textile fabric having a durable antibacterial if finishir'esistant to washing with water comprising cotton amounts such that the fabric contains at least 0.0001

' percent by weight of neomycin.

V finish resistant to washing 10. A dry textile fabric having a with water comprising nylon fibers having uniformly adsorbed thereon neomycin in amounts such that the fabric contains at least 0.0001

percent by weight of neomycin.

11. A dry textile fabric having a acrylic fibers having uniformly adsorbed thereon neo-. mycin in amounts such that the fabriccontains at least 0.70001 percent by weight of neomycin.

12. A dry textile fabric having a durable antibacterial finish resistant to washing with water comprising polyacrylonitrile fibers having uniformly adsorbed thereon neomycin in amounts such that the fabric contains at least 0.0001 percent by weight of neomycin.

References. Cited in the file of this patent i UNITED STATES PATENTS 2,680,701 Cusumano June 8, 1954 7 OTHER REFERENCES Regna' et al.: The Isolation of Neomycin B, I .Am. Chem. .S oc., February 1950, pp. 1045-1046. Waksrnan: Neornycin, Rutgers Univ. Press,

durable antibacterial durable antibacterial finish resistant to washing with water comprising poly-T 

1. A METHOD OF IMPARTING A DURABLE ANTIBACTERIAL FINISH TO TEXTILE FIBERS WHICH COMPRISES THE STEPS OF BRINGING SAID FIBERS INTO CONTACT WITH AN AQUEOUS SOLUTION CONTAINING FROM AT LEAST 0.0001 PERCENT BY WEIGHT OF NEOMYCIN AND THEREAFTER DRYING SAID FIBERS. 